Liquid suspensions and powders of cerium oxide particles and polishing applications thereof

Abstract

Suspensions of cerium oxide particles in which the particles (secondary particles) have an average size not exceeding 200 nm, such secondary particles being comprised of primary particles having an average size not exceeding 100 nm with a standard deviation having a value not exceeding 30% of the value of this average size, are prepared from a solution of a cerium-III salt, including cerium IV or hydrogen peroxide, which is contacted with a base in the presence of nitrate ions and in an inert atmosphere; the medium thus obtained is subjected to a thermal processing in an inert atmosphere, then acidified and scrubbed and the powder is obtained by drying and calcining of the suspension, which suspension and powder are useful for polishing applications.

1. A suspension of cerium oxide particles in a liquid phase, said particles being secondary particles having an average size of at most 200 nm, and said secondary particles comprising primary particles whose average size is at most 100 nm with a standard deviation of at most 30% of the value of said average size of said primary particles. 
     
     
       2. The cerium oxide suspension as defined by  claim 1 , wherein the primary particles have sizes which exhibit a standard deviation of at most 20% of the value of said average size of said primary particles. 
     
     
       3. The cerium oxide suspension as defined by  claim 2 , wherein the primary particles have sizes which exhibit a standard deviation of at most 10% of the value of said average size of said primary particles. 
     
     
       4. The cerium oxide suspension as defined by  claim 1 , wherein the primary particles have sizes which exhibit an average value of at most 80 nm. 
     
     
       5. The cerium oxide suspension as defined by  claim 4 , wherein the primary particles have an average size of at least 30 nm. 
     
     
       6. The cerium oxide suspension as defined by  claim 1 , wherein the secondary particles have a dispersion index of at most 0.5. 
     
     
       7. The cerium oxide suspension according to  claim 6 , wherein the secondary particles have a dispersion index of at most 0.4. 
     
     
       8. The cerium oxide suspension as defined by  claim 1 , wherein the secondary particles have an average size of at most 150 nm. 
     
     
       9. The cerium oxide suspension as defined by  claim 1 , wherein the liquid phase comprises water. 
     
     
       10. The cerium oxide suspension as defined by  claim 1 , wherein the liquid phase comprises an organic solvent. 
     
     
       11. A process for preparing a cerium oxide suspension as defined by  claim 1 , comprising the following steps:
 (a) providing a solution of a cerium III salt which also comprises cerium IV; 
 (b) treating this solution with a base, under an inert atmosphere, whereby a precipitate is obtained; 
 (c) subjecting the medium obtained in the preceding step to a thermal treatment under an inert atmosphere, at least one of the steps (a), (b) or (c) being carried out in the presence of nitrate ions; and 
 (d) acidifying and washing the medium thus obtained, whereby the suspension is obtained. 
 
     
     
       12. The process as defined by  claim 11 , wherein the solution of a cerium III salt of step (a) comprises cerium IV in a cerium IV/cerium III molar proportion of from 1/5,000 to 1/50. 
     
     
       13. The process as defined by  claim 11 , wherein the content of nitrate ions during at least one of the steps (a), (b) or (c), expressed by the NO 3   31 /Ce 3+ molar ratio, ranges from 1/3 to 5. 
     
     
       14. The process for preparing a cerium oxide suspension as defined by  claim 1 , comprising the following steps:
 (a) providing a solution of a cerium III salt which also comprises aqueous hydrogen peroxide; 
 (b) contacting this solution with a base, under an inert atmosphere, whereby a precipitate is obtained; 
 (c) subjecting the medium obtained in the preceding step to a thermal treatment under an inert atmosphere, at least one of the steps (a), (b) or (c) being carried out in the presence of nitrate ions; and 
 (d) acidifying and washing the medium thus obtained, whereby the suspension is obtained. 
 
     
     
       15. The process as defined by  claim 14 , wherein the solution of the first step contains aqueous hydrogen peroxide in an H 2 O 2 /CeIII molar proportion ranging of from 1/10,000 to 1/100. 
     
     
       16. The process as defined by  claim 11 , wherein the thermal treatment is carried out at a temperature of at most 95° C. 
     
     
       17. The process for preparing a cerium oxide suspension, comprising contacting a suspension as defined by  claim 1  with an organic solvent. 
     
     
       18. A redispersible powder of cerium oxide particles, which, after redispersion in a liquid phase, provides a suspension as defined by  claim 1 . 
     
     
       19. A process for polishing a substrate, the said process comprising applying to the substrate, as the polishing agent therefor, the cerium oxide suspension as defined by  claim 1 . 
     
     
       20. The cerium oxide suspension as defined by  claim 1 , wherein the primary particles have sizes which exhibit an average value of at least 20 nm. 
     
     
       21. The cerium oxide suspension as defined by  claim 1 , wherein the primary particles have sizes which exhibit an average value of at least 10 nm. 
     
     
       22. The cerium oxide suspension as defined by  claim 1 , wherein the primary particles have sizes which exhibit an average value of at most 100 nm. 
     
     
       23. The cerium oxide suspension as defined by  claim 1 , wherein the primary particles have sizes which exhibit an average value of at most 60 nm. 
     
     
       24. The cerium oxide suspension as defined by  claim 1 , wherein the suspension is stable.